Date of Award

1-1-2010

Document Type

Campus Access Thesis

Department

Chemistry and Biochemistry

Sub-Department

Chemistry

First Advisor

Stanley M. Angel

Abstract

This thesis describes the use of various Raman spectroscopy techniques for the detection of N-acyl homoserine lactones (AHLs), which are quorum sensing molecules used in bacterial communication. The advantage of using Raman spectroscopy over other techniques is the possibility of in-situ detection of these molecules within their natural environment. The biggest issue to overcome is that Raman scattering is weak, and AHL molecules exist naturally at very low concentrations. Therefore, enhanced Raman techniques such as surface-enahanced Raman spectroscopy (SERS) and resonance Raman spectroscopy (RRS) are the focus of this research.

Surface-enhanced Raman measurements of AHLs were performed using silver colloids. Several different silver colloid synthetic procedures were used in order to determine which colloids are more suitable for AHL detection. During the course of these studies an unknown substance was discovered that competes with the AHL for adsorption to the silver surface. The unknown substance remained despite using different colloids and synthesis procedures. Literature was found that also supports the presence of this same unknown substance when using silver colloids for other types of SERS measurements.

UV Raman spectroscopy using a 244nm laser was also investigated for AHL measurements. Transmittance experiments showed that the AHLs absorb strongly at 244nm indicating the possibility of resonance enhancement. Concentration dependent studies showed that increasing concentration had virtually no effect on the Raman signal intensities due to a decrease in effective pathlength with increasing AHL concentration. Conclusions were drawn as to whether resonance or preresonance Raman enhancement occurred, and the technique was critiqued regarding in-situ AHL detection.

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